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  • 1
    Electronic Resource
    Electronic Resource
    A simple correction to final state energies of doublet radicals described by equation-of-motion coupled cluster theory in the singles and doubles approximation (1996)
    Springer
    Theoretical chemistry accounts 93 (1996), S. 303-313 
    Details
    ISSN: 1432-2234
    Keywords: Energy correction ; Doublet radicals ; Singles approximation ; Doubles approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A computationally inexpensive energy correction is suggested for radicals described by the equation-of-motion coupled cluster method for ionized states in the singles and doubles approximation (EOMIP-CCSD). The approach is primarily intended for doublet states that are qualitatively described by Koopmans' approximation. Following a strategy similar to those used in multireference coupled cluster theory, the proposed correction accounts for all correlation effects through third order in perturbation theory and also includes selected contributions to higher-order energies. As an initial test of the numerical performance of the method, total energies and energy splittings are calculated for some small prototype radicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01127508
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A simple correction to final state energies of doublet radicals described by equation-of-motion coupled cluster theory in the singles and doubles approximation (1996)
    Springer
    Theoretica chimica acta 93 (1996), S. 303-313 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Energy correction ; Doublet radicals ; Singles approximation ; Doubles approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  A computationally inexpensive energy correction is suggested for radicals described by the equation-of-motion coupled cluster method for ionized states in the singles and doubles approximation (EOMIP-CCSD). The approach is primarily intended for doublet states that are qualitatively described by Koopmans’ approximation. Following a strategy similar to those used in multireference coupled cluster theory, the proposed correction accounts for all correlation effects through third order in perturbation theory and also includes selected contributions to higher-order energies. As an initial test of the numerical performance of the method, total energies and energy splittings are calculated for some small prototype radicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01127508
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    The ACES II program system (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 879-894 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ACES II, a new program system for ab initio electronic structure calculations is described. The strengths of ACES II involve the use of many-body perturbation theory (MBPT) and coupled-cluster (CC) theory for calculating the energy, geometry, spectra, and properties of small- to medium-sized molecules. This paper gives a brief overview of the ACES II project, describes many features of the program system, and documents a number of benchmark calculations. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560440876
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    On the convergence of MBPT and CC nuclear magnetic shielding constants of BH toward the full CI limit (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 437-442 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The performance of many-body perturbation theory (MBPT) and coupled-cluster (CC) methods in the calculation of nuclear magnetic shielding constants for BH is analyzed by comparison with results from full configuration interaction (FCI) calculations. Low-order MBPT computations are shown to be inadequate for BH, while the coupled-cluster ansatz, in particular, in its singles and doubles (CCSD) approximation, provides an efficient treatment of electron correlation, overestimating correlation effects to the 11B shielding by only 3-4 ppm (1.5%). Based on this comparison, CCSD calculations with large atomic natural orbital (ANO) basis sets are used to estimate accurate theoretical values for the isotropic and anisotropic shielding constants of BH. © 1995 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560847
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    An unconventional scf method for calculations on large moleculesThis paper is dedicated to Prof. John A. Pople on the occasion of his sixtieth birthday. Over the years, we have benefitted significantly from his excellent contributions to Quantum Chemistry and his pragmatic way of solving quantum chemical problems. (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 7 (1986), S. 274-282 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An unconventional SCF method for calculations on large molecules with more than 100 basis functions is described. Storage problems which arise in conventional SCF schemes when storing more than 107 integrals are avoided by repeated calculation of integrals. The resulting increase in computational times is kept at a reasonable level by (a) improving the initial guess, (b) accelerating convergence, (c) employing a recursive construction of the Fock matrix, and (d) eliminating insignificant integrals from the calculation by a density-weighted cutoff criterion. Sample calculations show that, compared with conventional SCF calculations, computational times increase by 25%-75% depending on the basis set and the shape of the molecule.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540070305
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    Paper (German National Licenses)
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